Angst: One or more character may be dealing with a great amount of pain or loss, there is much conflict.
Citrus: Less graphic than lemon. Citruses may hint at sex or casually mention it.
Lemons: Most of the time lemons are graphically-termed sex scenes that describe everything that is happening to both characters. This is a fairly loose definition.
Lime: Going a little furthur than citrus. Lime is a wide category that could apply to many things that happen between lovers, but nothing graphic.
Shimegami: Fairly close to Duo's "Shinigami," Shimegami means "Goddess of Death."
Shounen-ai: Literal translation, "boy love." Usually is more romantic situations and such than yaoi, no graphic scenes.
Yaoi: Homosexual relationships between two males. Usually yaoi is more hardcore than shounen-ai and may include sex scenes or very descriptive terms. Not reccommended for those younger than 17.
Yuri: Homosexual relationships between two females. May include sex scenes or descriptive terminology.